A typical gas turbine engine includes one or more turbine rotors configured to extract energy from a flow of combustion gases directed through the engine. Each rotor includes an annular array of blades coupled to a rotor disk. The radially outermost boundary of the flowpath through the rotor is defined primarily by a turbine shroud, which is a stationary structure that circumscribes the tips of the blades. As is generally understood, the various rotor components operate in an extremely high temperature environment and it is often required that the components be cooled by an air flow to ensure adequate service life. Typically, the air used for cooling is extracted (or bled) from the compressor, which negatively impacts the specific fuel consumption (“SFC”) of the gas turbine engine.
In the past, it has been proposed to replace metallic shroud structures with materials having improved high-temperature capabilities, such as ceramic matrix composite (CMC) materials. These materials have unique mechanical properties that must be considered during the design and application of a turbine component, such as a shroud segment. For example, when compared to metallic materials, CMC materials have relatively low tensile ductility or low strain to failure, and a low coefficient of thermal expansion (“CTE”).
One type of segmented CMC shroud incorporates a rectangular “box” design. Box shroud segments typically include an outer wall, an inner wall and first and second sidewalls extending between the inner and outer walls to form a complete rectangular-shaped cross-section. The outer wall is disposed on the casing-side of the turbine shroud and forms the radially outermost portion of the shroud segment. The inner wall is disposed on the flowpath-side of the turbine shroud and forms the radially innermost portion of the shroud segment. As such, the inner wall defines the radial outer flowpath boundary for the combustion gases flowing through the rotor.
Given the direct exposure of the inner wall of the shroud segment to the hot gases flowing through the rotor as comparted to the shielded position of the outer wall of the shroud segment, a significant thermal gradient often exists between the inner wall and the outer wall. As a result, the inner and outer walls thermally expand and contract at differing rates. Such differing expansion/contraction rates cause thermally-induced strain within the shroud segment, which can significantly impact the component life of the segment. This is particularly true for gas turbine engines having turbine shrouds exposed to extremely high thermal gradient conditions.
Accordingly, an improved shroud segment assembly that incorporates expansion joints to allow one or more of the segment walls or sides to expand and/or contract independent from other segment walls/sides so as to provide a reduction in the resulting thermally-induced strain within the assembly would be welcomed in the technology.